A characteristic of Myotonic Dystrophy is
the wide variability of its expression. Certain
individuals will be very affected by the disease while
others will show very little signs of it. Certain
individuals can also be carriers of the genetic anomaly
but show no sign at all of the disease. This variability
is seen within different families as well as within the
same family. Generally, the overall severity of the disease
can be predicted by the age at which it first manifests, of its clinical
signs, and of its evolution. Earlier onset of the disease
brings greater chances of being highly affected by it.
The median age for onset of the disease
is 20 to 25 years of age but since there is great variability and
since symptoms sometimes go unnoticed, the disease is
often undiagnosed until later, when the patients are in their
forties. In addition to the classic form of the disease
(above), there are early forms of the disease (juvenille)
and the disease can manifest at birth (congenital form).
presentation will describe the principal signs/symptoms
of the disease.
Muscle weakness mainly
affects the head and neck and then moves to the
extremities. This weakness is responsible for
mastication problems. When this weakness is severe it
causes a slack jaw and open mouth. Usually face muscle
weakness will cause droopy eyelids. Weakness of the
palate, tongue and vocal cords is responsible for a
change in voice quality that then becomes nasal.
Weakness of the muscles of the pharynx can bring on dysphagia (difficulty swallowing) to different degrees.
Atrophy and weakness of neck muscles is frequent. This
weakness causes difficulty with lifting the head from
the pillow and can ultimately cause an anterior flexing
of the head (bent toward the back).
When chest muscles are affected,
respiratory amplitude can be reduced which may bring on
chronic respiratory failure. Weak abdominal muscles will
cause a slight pouch.
The muscles of the extremities are the
most affected. Weakness and atrophy affects the lower
leg muscles and causes droopy feet. Regarding the arms,
weakness mostly affects the forearms and hands and in
particular the fingers and wrists.
During the evolution of the disease
muscle weakness can extend to the shoulders and pelvic
It is a
lack of muscle release after a sustained contraction.
It is painless, stimulated by the cold, by fatigue and
reduced by heat and repetitive movements. It disappears
during sleep. Subjects often describe the phenomenon by
saying: “My hands lock up”. Myotonia can be clearly seen
by asking the subject to squeeze his/her hand and then
rapidly release. Subjects with the disease are unable to
open their hand quickly. The phenomenon can also be provoked by
tapping the muscle sharply, known as percussion.
The principal ocular manifestations that
are observed in this disease are cataracts that are
present in nearly 100% of patients and can sometimes be
the only sign of the disease. Other ocular
manifestations such as diplopia (double vision),
intra-ocular hypotension and keratites are non specific
to the disease.
Cardiac manifestations :
Trouble with cardiac
rhythm and conduction will arise first and can cause
shortness of breath, discomfort, palpitations, syncope
(brief loss of consciousness) and in severe cases,
sudden death. Certain studies rate the risk of sudden
death at 10%.
Other manifestations of the disease:
A certain degree of
baldness is frequently observed in the men affected by
the disease. Baldness is otherwise very rare in women.
From an endocrine perspective, men affected by the
disease often suffer from testicular atrophy that does
not result in infertility. Hypersensitivity to insulin
resulting from a peripheral resistance to insulin is
present, but no diabetes is linked to the disease.
Reduced hearing is frequently observed but often
overlooked. It can be verified by audiometric tests.
Regarding digestion, signs are inconsistent and range
from difficulty with swallowing to constipation. Biliar
lithiasis (gallstones) can be observed and will cause about
a third of the patients to undergo a cholecystectomy.
Regarding behaviour, the disease can
cause a reduction in activities (hypoactive individual)
and sometimes the presence of great fatigue/drowsiness
is present and can be very detrimental to professional
life. There is sometimes a manifestation of sleep apnoea
but it does not seem to be the cause of the great
fatigue/drowsiness that is present in the majority of
Myotonic Dystrophy and pregnancy :
and delivery can present certain dangers for women
affected by this disease. The principal complications
observed during pregnancy are a high rate of
miscarriages, premature births and complications at
delivery. Infant mortality is also elevated and
estimated at 160/1000 births compared to 19/1000 births
within the population not suffering from the disease.
One of the great risks of pregnancy for a
woman suffering from Myotonic Dystrophy is the chance of
giving birth to a child with the congenital form of the
disease. This can manifest in a severe form including
congenital malformations and significant respiratory
distress that can cause the death of the infant within
the first days or months of life. The congenital form of
the disease can sometimes be less severe in which case
the infant will be hypotonic (floppy baby), have trouble
swallowing and evolving into slow muscle development and
severe mental retardation. The congenital form is only
seen when the woman is affected by the disease. Some
rare cases have been reported in cases where the father
was affected by the disease but they remain exceptional.
In 1994, a particular form of Myotonic
Dystrophy with a different genetic anomaly than classic
Myotonic Dystrophy (DM1) was described. Since the
proximal (near) muscles were mainly affected by this form of
the disease it was first called Proximal Myotonic
Myopathy (PROMM) and then Type 2 Myotonic Dystrophy
because of its similarities to Steinert Disease.
Muscle weakness and atrophy:
weakness affects face and neck muscles but is much less
severe than in DM1. Regarding limbs, muscle
weakness mostly affects the hips and shoulders. Moderate
weakness in the feet and hands can happen as the disease
evolves but is rarely an early symptom. Muscular atrophy
is moderate in this form of Myotonic Dystrophy. In fact,
hypertrophy of the calf muscles (elongation) is often
observed in this form of the disease.
Myotonia is often
described by affected subjects as the locking up of
hands. It is moderate and not very debilitating.
Myotonia is much more variable over time than in the DM1
Muscle pain is frequent but unrelated to
the severity of the myotonia or with exercise.
develop before the age of 50 and have the same
characteristics as those associated with DM1.
Cardiac manifestations :
problems are far less frequent than in DM1. They are
limited to First-Degree atrioventricular blocks or
branch blocks. Cardiac complications are generally less
severe although some cases of sudden death have been
reported. Pacemaker implants and severe
arrhythmia have also been reported. Contrary to DM1, there is no manifestation
of respiratory failure.
Cerebral manifestations :
The disease’s effect on
executive function is similar to that observed in DM1
although much less severe. Personality changes can be
observed as well as poor performance concerning certain
functions. There is no mental retardation linked to this
form of Myotonic Dystrophy as there is in the congenital
and early forms of DM1.
atrophy is sometimes present in men as well as a
peripheral resistance to insulin but these
manifestations are less severe than in MD1. There is no
available data linking thyroid disease and DM2.
Pregnancy is an aggravating factor for pain, myotonia
and muscle cramps. Affected subjects often complain of